1. Fit-for-Purpose Ki-67 Immunohistochemistry Assays for Breast Cancer.
- Author
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Torlakovic EE, Baniak N, Barnes PJ, Chancey K, Chen L, Cheung C, Clairefond S, Cutz JC, Faragalla H, Gravel DH, Dakin Hache K, Iyengar P, Komel M, Kos Z, Lacroix-Triki M, Marolt MJ, Mrkonjic M, Mulligan AM, Nofech-Mozes S, Park PC, Plotkin A, Raphael S, Rees H, Seno HR, Thai DV, Troxell ML, Varma S, Wang G, Wang T, Wehrli B, and Bigras G
- Subjects
- Humans, Female, Biomarkers, Tumor metabolism, Biomarkers, Tumor analysis, Canada, Sensitivity and Specificity, Tissue Array Analysis methods, Ki-67 Antigen metabolism, Ki-67 Antigen analysis, Breast Neoplasms metabolism, Breast Neoplasms diagnosis, Breast Neoplasms pathology, Immunohistochemistry methods
- Abstract
New therapies are being developed for breast cancer, and in this process, some "old" biomarkers are reutilized and given a new purpose. It is not always recognized that by changing a biomarker's intended use, a new biomarker assay is created. The Ki-67 biomarker is typically assessed by immunohistochemistry (IHC) to provide a proliferative index in breast cancer. Canadian laboratories assessed the analytical performance and diagnostic accuracy of their Ki-67 IHC laboratory-developed tests (LDTs) of relevance for the LDTs' clinical utility. Canadian clinical IHC laboratories enrolled in the Canadian Biomarker Quality Assurance Pilot Run for Ki-67 in breast cancer by invitation. The Dako Ki-67 IHC pharmDx assay was employed as a study reference assay. The Dako central laboratory was the reference laboratory. Participants received unstained slides of breast cancer tissue microarrays with 32 cases and performed their in-house Ki-67 assays. The results were assessed using QuPath, an open-source software application for bioimage analysis. Positive percent agreement (PPA, sensitivity) and negative percent agreement (NPA, specificity) were calculated against the Dako Ki-67 IHC pharmDx assay for 5%, 10%, 20%, and 30% cutoffs. Overall, PPA and NPA varied depending on the selected cutoff; participants were more successful with 5% and 10%, than with 20% and 30% cutoffs. Only 4 of 16 laboratories had robust IHC protocols with acceptable PPA for all cutoffs. The lowest PPA for the 5% cutoff was 85%, for 10% was 63%, for 20% was 14%, and for 30% was 13%. The lowest NPA for the 5% cutoff was 50%, for 10% was 33%, for 20% was 50%, and for 30% was 57%. Despite many years of international efforts to standardize IHC testing for Ki-67 in breast cancer, our results indicate that Canadian clinical LDTs have a wide analytical sensitivity range and poor agreement for 20% and 30% cutoffs. The poor agreement was not due to the readout but rather due to IHC protocol conditions. International Ki-67 in Breast Cancer Working Group (IKWG) recommendations related to Ki-67 IHC standardization cannot take full effect without reliable fit-for-purpose reference materials that are required for the initial assay calibration, assay performance monitoring, and proficiency testing., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)
- Published
- 2024
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